/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.opensymphony.xwork2.inject;

/**
 * 依赖的mapping key。通过type和name形成的唯一id
 * 构造器需要type和name两个参数
 * 因为在ContainerImpl 类中 ，该类要当做map的key使用
 * 所以重写了hashCode与equals 并在构造方法中计算hashCode,值得学习 ，还有equals方法
 * Dependency mapping key. Uniquely identified by the required type and name.
 *
 * @author crazybob@google.com (Bob Lee)
 */
class Key<T> {

  final Class<T> type;
  final String name;
  final int hashCode;

  /**
   * 很奇怪  这个构造方法是私有的？？
   * 哦，下面有个newInstance方法调用之
   * 并且这个newInstance方法对外暴露
   * @param type
   * @param name
   */
  private Key(Class<T> type, String name) {
    if (type == null) {
    	
    	//向这种通过判断抛空指针异常的时候  写上谁是null
      throw new NullPointerException("Type is null.");
    }
    if (name == null) {
      throw new NullPointerException("Name is null.");
    }

    this.type = type;
    this.name = name;

    hashCode = type.hashCode() * 31 + name.hashCode();
  }

  Class<T> getType() {
    return type;
  }

  String getName() {
    return name;
  }

  @Override
  public int hashCode() {
    return hashCode;
  }

  @Override
  public boolean equals(Object o) {
    if (!(o instanceof Key)) {
      return false;
    }
    if (o == this) {
      return true;
    }
    
    // 这个equals方法比较号写的原因是在构造方法的地方限制了name和type这个两个属性不会为null
    Key other = (Key) o;
    return name.equals(other.name) && type.equals(other.type);
  }

  @Override
  public String toString() {
	  
	  /**
	   * 良好的toString 方法使得debug更容易
	   * 也与Effiective Java中提到的吻合
	   */
    return "[type=" + type.getName() + ", name='" + name + "']";
  }

  static <T> Key<T> newInstance(Class<T> type, String name) {
    return new Key<T>(type, name);
  }
}
